The adipose conversion of 3T3 cells is being examined under simple cell culture conditions. It appears to be one of the simplest forms of mammalian differentiation. It is independent of cell-cell interactions but is subject to control by hormones and possibly other factors. The system is being examined as a model for fat cell formation in animals. BIBLIOGRAPHIC REFERENCES: H. Green and O. Kehinde: Spontaneous Heritable Changes Leading to Increased Adipose Conversion in 3T3 Cells. Cell 7:105-113, 1976. H. Green: The Resting and Growing States of the Fibroblasts. In Advances in Pathobiology 4, Cancer Biology. II. Etiology and Therapy. C.M. Fenoglio and D.W. King (eds), Stratton Intercontinental Medical Book Corp., N.Y>, 1976.